Will be required for new checkpoints code and later governor
implementation.

Used for checkpointing logic in bonding state checkpoints

Handles historic checkpointing ("snapshotting") and lookup
of the bonding state.

 - unit tests
 - integration tests
 - gas-report
 - fork test for upgrade

This will provide a cleaner experience using governance
tools, since users that don't have any stake won't get
errors when querying their voting power. For users that
do have stake, we will make sure to checkpoint them on
first deploy.

100% coverage 😎

"Harness" seems to make more sense, I could only think
of that now.

Co-authored-by: Chase Adams <[email protected]>

Meaning the start of next round instead of the
current round. This is more compatible with the
way OZ expects the timepoints to work in the clock
and snapshots on the Governor framework.

This changes the BondingVotes implementation to
stop having so many reverts on supposedly invalid states.

Instead, redefine the voting power (and checkpointed stake)
as being zero before the first round to be checkpointed.

This had other implications in the code like removing
changes in BondingManager to make the state complete
(always having an earnings pool on lastClaimRound).
Instead, the BondingVotes implementaiton is resilient
to that as well and just assumes reward() had never
been called.

This also fixed the redundant reverts between BondingVotes
and SortedArrays, as now there are almost no reverts.

Just for consistency with other contracts.
Some docs as a bonus

This is to increase compatibility with some tools
out there like Tally, which require only these
functions from the ERC20 spec, not the full implementation.

So we can have these from the get-go to make things
easier if we want to make something with them.